1. Field of the Invention
The present invention relates to fluoropolymers and, in particular, relates to fluoropolymer compositions having improved properties, such as coatings of the type that may be applied to either rigid or flexible substrates in which a non-stick and/or abrasion resistant surface is desired. In particular, the present invention relates to fluoropolymer compositions that include multiple fluoropolymer components and may be used to form coatings having improved non-stick or release characteristics and/or improved abrasion resistance, as well as films and/or blended powder compositions.
2. Description of the Related Art
Fluoropolymers are long-chain polymers comprising mainly ethylenic linear repeating units in which some or all of the hydrogen atoms are replaced with fluorine. Examples include poly tetrafluoroethylene (PTFE), methylfluoroalkoxy (MEA), fluoro ethylene propylene (FEP), perfluoroalkoxy (PEA), poly(chlorotrifluoroethylene) and poly(vinylfluoride).
Non-stick coating systems including fluoropolymers are applied in single or multiple coats to the surface of a substrate to provide a coated substrate having a non-stick coating to which extraneous materials will not adhere. In a multiple layer coating system, the non-stick coating generally includes a primer and a topcoat, and optionally, one or more midcoats.
The use of non-stick coating systems which are applied to a substrate in multiple layers has been known for many years. The primers for such systems typically contain a heat resistant organic binder resin and one or more fluoropolymer resins, along with various opaque pigments and fillers. The midcoats contain mainly fluoropolymers with some amounts of opaque pigments, fillers and coalescing aids, while the topcoats are almost entirely composed of fluoropolymers, such as entirely high molecular weight polytetrafluoroethylene (HPTFE), or HPTFE with a small amount of a melt-processible fluoropolymer.
Glasscloth is one example of a flexible substrate that may be coated with a fluoropolymer coating. The coating typically includes a high molecular weight polytetrafluoroethylene (HPTFE), either by itself or including small amounts of additional polymers and/or fillers. One coating technique involves feeding a glasscloth web through a dip tank containing a dispersion of the fluoropolymer, and then feeding the coated web upwardly through a drying and sintering oven tower to cure or fix the coating. This process is usually repeated a number of times whereby up to 10 or more coating layers may be applied.
What is needed are improved fluoropolymer compositions for applications such as coatings for rigid and/or flexible substrates that demonstrate improved characteristics, such as improved release and/or abrasion resistance.